The present invention generally relates to rotating equipment such as electric motors and generators, and more particularly, to an electric generator rotor and to a rotor feature that may minimize stress in the rotor and may reduce maintenance and repairs to the rotor.
An electric generator may have a rotor rotating within a magnetic field and having poles carrying coil windings. The coil windings may generate electric current as they move through the magnetic field.
The coil windings wrap around rotor poles extending radially from a central rotor shaft. Rotor rotation creates a radially-outward force that biases the coil windings to move away from the central shaft. To keep the coil windings in place during rotation, the poles have overhangs extending perpendicularly outward from the poles and distal the central shaft. The overhangs block the coil windings from slipping outward off of the poles while the rotor rotates.
Poles may experience high stresses at an interior corner where the overhang extends out from the pole. The high stresses may be caused by a combination of the radially-outward force on the coil winding and bending caused by the radially outward force on the overhang.
As may be seen in the prior art, there have been attempts to address high stress in rotors. In one example, an oversized conventional fillet is added only to certain regions where high stress is expected. A conventional fillet eliminates the interior sharp corner that results from the intersection of two planar faces by adding material to the corner in the shape of a concave curvilinear profile that intersects tangentially with both faces. The fillet eliminates the sharp corner that acts as a stress concentration but also blocks access to the corner so that any mating parts may be offset from both the planar faces. It is well known in the art to utilize a larger conventional fillet to reduce stress concentrations.
In another example, a configuration used in current rotor pole production and as a method of repairing cracks at the junction between the overhang and the pole comprises removing material around the crack to create an oversized stress-relief fillet. The fillet in this example does not intersect either of the surfaces tangentially.
In both of the abovementioned examples, a fillet with a large radius is utilized to maintain reasonable pole fillet stress levels.
As is seen, there is a need for an improved stress-reducing fillet for generator rotors.